Bioavailability is the degree to which a therapeutic agent becomes available to the target tissue after administration. Many factors can affect bioavailability including the dosage form and various properties, e.g., dissolution rate of the therapeutic agent. Poor bioavailability is a significant problem encountered in the development of pharmaceutical compositions, particularly those containing an active ingredient that is poorly soluble in water. Poorly water soluble therapeutic agents, i.e., those having a solubility less than about 10 mg/ml, tend to be eliminated from the gastrointestinal tract before being absorbed into the circulation. Moreover, poorly water soluble therapeutic agents tend to be unsafe for intravenous administration techniques, which are used primarily in conjunction with fully soluble therapeutic or diagnostic agents.
Nanoparticles, described in U.S. Pat. No. 5,145,684, are particles consisting of a poorly soluble therapeutic or diagnostic agent onto which are adsorbed a non-crosslinked surface modifier, and which have an average particle size of less than about 400 nanometers (nm). These nanoparticles provide for increased bioavailability and for imporved diagnostic charactistics compared to other materials having larger sizes.
In U.S. Pat. No. 4,534,959, there is described a composition in an aersol container. When sprayed the composition gels on the surface of living tissue. This composition contains a polyoxyethylene-polyoxypropylene copolymer. However the copolymer must be present in high percentage. Further, the therapeutic agent must be solubilized. U.S. Pat. No. 3,867,533 relates to another aqueous gel composition; U.S. Pat. No. 4,465,663 is similar and relates to cosmetic gels.
A wide variety of surface modifiers are described in the '684 patent and in subsequent patents and applications that relate to nanoparticles as described therein. However, there is a continuing need for surface modifiers that have rehological properties that make them particularly advantageous for a variety of uses.